The present invention relates generally to the field of steam generators and in particular to a new and useful link type seismic tie for a boiler system for absorbing and dissipating seismic force or energy to limit the displacement of the boiler system, including support steel frames and piping.
During an earthquake, seismic energy is dissipated by damping due to plastic behavior of the structural system. The structural system consists of the supporting structural steel, boiler ties, and the boiler itself. Using certain techniques, the structural steel may be designed to enhance damping by plastic behavior. However, it is not practical to configure the boiler for enhanced plastic behavior. This is because the boiler's overall configuration is governed by the pressure part design and arrangement.
There are a variety of seismic ties currently available for dissipating seismic energy or forces. A typical link-type seismic tie is shown in FIG. 1, wherein two link members 32, 33 are attached by pins to a buckstay beam 36 at one end and structural steel 37 at the other. Finger plates 38, as shown in FIG. 2, are typically located in the ends of the buckstay beam 36 to further dissipate seismic energy by plastic behavior.
Japanese Patent JP6002804 to Minoru et al. discloses a link-type seismic tie comprising two link members arranged separately in a horizontal direction and two vertical pin members connecting both ends of the upper and lower link members. One of the pin members is attached to a bracket for connection to a supporting iron frame and the other pin member is attached to a buckstay connected to a boiler main body.
Japanese Patent 9112805 also discloses a supporting structure for load reduction of a boiler during an earthquake. The supporting structure includes a pair of links arranged between and connected to a pair of binders wherein one of the binders is attached to a buckstay of a boiler and the other binder is attached to a support structure. Elastic-plastic elements are provided between the binders and parallel to the links. The elastic-plastic elements contain a rounded diamond-shaped opening. A sheer plate is secured between the binders but faces in a direction perpendicular to the direction that the elastic-plastic elements face. Relative displacement caused by an earthquake, causes the binder near the buckstay to deform the elastic-plastic elements and the sheer plate, generating a restriction force. The involvement of the sheer plate in generating the restriction force reduces the number of elastic-plastic elements required.
U.S. Pat. No. 4,940,025 to Ott et al. discloses a steam generator support arrangement for loading forces resulting from seismic accidents. The support arrangement is provided between a ring girder encircling the steam generator and a concrete housing, and includes a pair of V-shaped link arrangements hinged at an apex and a snubber arranged between the link arrangements and connected to the apexes of the link arrangements.
Japanese Patent 5141607 discloses an assembly for transmitting furnace internal pressure from a buckstay to a supporting steel frame, absorbing the thermal expansion of the furnace pressurization. The assembly includes a coupling member attached to the buckstay. The coupling member is arranged between two separated link members, which lie along the same plane as the coupling member. The coupling member is attached to both link members at one end via a pin. Steel frames are attached to the link members via pins at the opposite end of the link members.
Japanese Patent 9178109 discloses a conventional prior art supporting structure for load reduction of the boiler during an earthquake. The supporting structure includes a pair of links connected to a pair of perpendicular binders which are a link mechanism for holding two or more elastic-plastic elements between a buckstay and a support frame, which are deformed upon the occurrence of an earthquake.
U.S. Pat. No. 4,286,549 to Eisinger discloses that it may be desirable to use rigid ties with springs and dampers for securing a steam generator to the upstanding members of a frame. The dampers react to displacement of components to which they are attached, to absorb energy as well as to carry load transmitted between the steam generator and frame. Springs are used as deformable structures.
U.S. Pat. No. 3,393,665 to Juchtern discloses a seismic tie attached to adjacent portions of a tube bank and furnace wall to limit relative movement and prevent distortion and damage to the furnace wall as a result of lateral forces caused by seismic disturbances for example.
The straight-bar link-type tie of the prior art provides only a very limited ability to dissipate seismic energy. At best, it may buckle providing some damping by plastically bending. However, this means of energy absorption is relatively ineffective and not easily or accurately predicted or controlled by design calculations. Also, unacceptably large boiler displacements may be necessary before any significant seismic energy would be absorbed.
In addition, because a large all-welded boiler is a very stiff body, it is important that damping plasticity be supplied at any location where it is possible to do so. One of the few possible locations at which damping may be added is where the boiler connects with the structural steel. The boiler tie links provide this location opportunity.
There is a need in the art for greater or more effective dissipation of seismic energy in connection with boiler seismic ties.